1. Field of the Invention
The present invention relates to crushable roadway crash cushions and, more specifically, those crash cushions which contain collapsible barrels, drums or like members.
2. Description of Related Art
A common highway crash cushion device is created by lining up a number of barrels which are formed of either metal or plastic. The lines of barrels are then positioned upstream of a fixed structure which is located in or adjacent to a roadway, the fixed structure representing a potential impact hazard to vehicles traveling along the roadway. The fixed structure is typically a concrete object, such as a bridge abutment or a median. In this discussion, the term "upstream" refers to the direction along the roadway from which traffic is expected to approach the fixed structure and, hence, is the direction from which a vehicle is most likely to impact the fixed structure. Conversely, "downstream" refers to the direction along the roadway which is generally opposite the upstream direction.
In conventional designs, barrels of a desired resistance to crushing are welded together at contact points and metal bands may be used to surround the barrels and band them together. Spacer bars or steel straps may also be tack welded to portions of the barrels. Screw eyes are screwed into the barrels so that wire rope or cables can be passed through the eyes and anchor the lines of barrels in position. It has also been known to place within the barrels a filler such as sand, sawdust and so forth, although normally the barrels remain unfilled. The barrels themselves are sometimes placed atop chair assemblies so that they remain above the ground. The upstream end of the lines of barrels is often covered by a reflectorized nose cover.
Some designs for barrel-filled crash cushions are described in U.S. Pat. No. 3,643,924, entitled "Highway Safety Device" issued to Fitch. Fitch shows a cushion formed of a group of barrels filled to varying degrees with sand.
One problem associated with conventional barrel cushions is their tendency to "pocket" at a critical impact point, thus causing the impacting vehicle to spin-out, creating a potential hazard to other traffic and failing to smoothly redirect the vehicle in a potentially controllable condition.
A further problem associated with the use of barrel crash cushions is that of "coffin corner" impacts. A coffin corner is a relatively angular portion of many fixed structures located near a roadway shielded by cushions. A gore wall, for example, usually presents two sharp (approximately 90.degree.) lateral corners which pose particular hazards for impacting vehicles. Vehicles which impact a conventional crash cushion near the position where the cushion adjoins the gore wall may cause the cushion to pocket at that point and permit the vehicle to impact the coffin corner resulting in increased penetration within the vehicle and high levels of deceleration.
A third, related problem associated with conventional barrel cushion design stems from the fact that the barrel cushion is primarily designed to cushion only impacts resulting from vehicles which approach the fixed structure from substantially the upstream direction. The cushions do not adequately cushion or smoothly redirect those vehicles which occasionally strike the cushion from the downstream direction or a direction other than primarily upstream. Because the lines of barrels in a typical conventional crash cushion are relatively thin (2-3 barrels in width), a vehicle may tear completely through the cushion after striking the side of the cushion. Widening the cushion appreciably by adding additional lines of barrels may be impractical in some situations, such as when the cushion is located on a narrow median strip.
Although there have been some design changes proposed in the past for barrel-type crash cushions, these modifications would not address all or most of the problems inherent in the design.
U.S. Pat. No. 3,845,936, issued to Boedecker, Jr. et al., for example, shows a modular crash cushion in which a series of overlapping sheet-like "fish scales" are affixed along the longitudinal sides of the barrel cushion to help divert a vehicle upon impact with the side of the crash cushion. Each of the fish scales is constructed of a plywood sheet and a painted metal sheet. Unfortunately, fish scales of this type do not properly redirect vehicles which impact the cushion from the downstream direction or a direction resulting in an impact which is other than substantially end-on. To this extent, the crash barrier is, at best, unidirectionally redirective, or redirective of impacts approaching from one direction--from substantially upstream. Further, the fish scales may themselves present a hazard to an impacting vehicle by causing it to become hung up on or be pierced by the sharp edges of the scales. Therefore, these types of barriers are not be suitable in situations where traffic passes by the cushion in two directions.
U.S. Pat. No. 4,583,716, issued to Stephens et al. describes an anchoring system in which buffer elements are positioned in an ordered array extending forwardly of a rigid backing member adjacent to a fixed structure. Diaphragm members are disposed in the array and extend laterally outward of the array at fixed intervals. Fender panels are pivotally coupled to opposed ends of the diaphragm members and extend rearwardly from their associated diaphragm members to partially overlap the fender panels coupled to succeeding diaphragm members. When this type of cushion is impacted from an end-on direction, the fender panels swing outwardly on their pivotal connections. Like those of the fish scales, the edges of the fender panels present a potential hazard for vehicles impacting the cushion from a direction other than substantially end-on.
Because of the problems with pocketing, coffin corner impacts, and non-end-on impacts, conventional barrel cushion designs will not meet new highway safety standards for the year 1998. Existing standards; Under National Cooperative Highway Research Program (NCHRP) Report 230, a typical barrel crash cushion is considered to be a non-redirective crash cushion. A redirective cushion or barrier is one which is substantially not penetrated by the vehicle and which acts to redirect the vehicle back into the flow of traffic. The impact performance requirements and, hence, the capabilities, of a nonredirective crash cushion are considerably less than those for a redirective crash cushion. A redirective crash cushion is subjected to more tests, and the requirements of those tests are more rigorous. A new standard, known as NCHRP Report 350, is expected to become effective on Sep. 1, 1998 and adopts more stringent requirements for such crash barriers.
A further drawback to conventional designs for barrel cushions is that the barrels and their metal banding connections are themselves unprotected and exposed to the impacts from vehicles. Thus, the connections may be broken and barrels nearest the roadway destroyed or damaged in light "brush by" collisions in which the cushion is not collapsed by the impact. "Brush by" collisions of this nature, therefore, require maintenance and repair of the cushion.
The present invention is directed to reducing the problems associated with prior art systems.